/*
 * Licensed to Elasticsearch under one or more contributor
 * license agreements. See the NOTICE file distributed with
 * this work for additional information regarding copyright
 * ownership. Elasticsearch licenses this file to you under
 * the Apache License, Version 2.0 (the "License"); you may
 * not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */
package org.elasticsearch.hadoop.mr;

import java.io.DataInput;
import java.io.DataOutput;
import java.io.IOException;
import java.lang.reflect.Field;

import org.apache.hadoop.io.ArrayWritable;
import org.apache.hadoop.io.NullWritable;
import org.apache.hadoop.io.Writable;
import org.elasticsearch.hadoop.util.ReflectionUtils;

// an array writable implementation that actually is writable
public class WritableArrayWritable extends ArrayWritable {

    static final Field VALUE_CLASS_FIELD;

    static {
        VALUE_CLASS_FIELD = ReflectionUtils.findField(ArrayWritable.class, "valueClass");
        ReflectionUtils.makeAccessible(VALUE_CLASS_FIELD);
    }

    public WritableArrayWritable(Class<? extends Writable> valueClass, Writable[] values) {
        super(valueClass, values);
    }

    public WritableArrayWritable(Class<? extends Writable> valueClass) {
        super(valueClass);
    }

    public WritableArrayWritable(String[] strings) {
        super(strings);
    }

    // constructor used by serialization only
    WritableArrayWritable() {
        super(NullWritable.class);
    }

    public void setValueClass(Class<Writable> valueClass) {
        ReflectionUtils.setField(VALUE_CLASS_FIELD, this, valueClass);
    }

    @Override
    public void readFields(DataInput in) throws IOException {
        String valueClass = in.readUTF();
        try {
            ReflectionUtils.setField(VALUE_CLASS_FIELD, this, Class.forName(valueClass, false, getClass().getClassLoader()));
        } catch (ClassNotFoundException ex) {
            throw new IOException("Cannot load class " + valueClass, ex);
        }
        super.readFields(in);
    }

    @Override
    public void write(DataOutput out) throws IOException {
        out.writeUTF(getValueClass().getName());
        Writable[] writables = get();
        // handle null - ArrayWritable does not
        if (writables == null) {
            out.writeInt(0);
        }
        else {
            super.write(out);
        }
    }
}